The present invention relates to a fuel injector assembly, and more particularly to an electronic fuel injector assembly which provides electronic control over mean injection pressure, and an internal combustion engine containing such a fuel injector assembly.
Conventional unit fuel injectors and pump-line-nozzle systems for use with, for example, Diesel engines, have various disadvantages. For example, the pressure during injection is dependent upon engine speed and load and the design of the injection cam lobe. Atomization of the fuel at the beginning of injection is often a function of a mechanical spring. Therefore, the quality of the atomization is a function of the reliability of the spring which may vary over time. In addition, the control of pressure at the beginning of injection is limited to the pre-load of the spring. Further, the flexibility of conventional unit injectors and pump-line-nozzle systems is limited to the extent that typically they do not include means to control pressure at the beginning of injection. In addition, conventional unit injectors and pump-line-nozzle systems typically require that the pressure be reduced in order to end injection. Such a reduction in pressure adversely affects the nature of fuel atomization which tends to increase particulate emission levels. Another disadvantage is that the speed with which conventional unit injectors and pump-line-nozzle systems operate when multiple injections are provided in a single engine cycle is limited due to the need to build pressure for each individual injection event during each single engine cycle. One drawback when using conventional common rail systems is that pressure waves from one injector tend to be xe2x80x9cseenxe2x80x9d by other injectors. This can lead to cylinder-to-cylinder variations as each injector is supplied with varying rail pressures. In addition, the injection pressure of conventional common rail systems is limited to about 1400 bar (20,400 p.s.i.). Such a pressure limitation limits fuel economy at high engine speeds and loads. Further, safety is always a concern when using high pressure. For example, in conventional common rail systems, the possibility that external high pressure lines and fittings may leak or rupture is always a concern. Similarly, the length of time that pressurized fuel is present at the needle tip is a concern since the tip may fail resulting in excessive fueling at the cylinder.
An object of the present invention is to provide a fuel injector assembly which combines advantages of a unit injector with those of a common rail fuel system.
Yet a further object of the present invention is to provide a fuel injection assembly which combines advantages of a unit injector and a common rail fuel system in one compact package.
Another object of the present invention is to provide a fuel injector assembly which combines peak injection pressure and injection rate shape of a unit injector with the mean injection pressure control of a common rail system over all engine speeds and loads.
A further object of the present invention is to provide a fuel injector assembly which provides quick pilot injection response and good atomization characteristics at the beginning and ending of injection found in a common rail system.
Yet another object of the present invention is to provide a fuel injector assembly which does not present the safety concerns of a conventional continuously pressurized needle.
Another object of the present invention is to provide a fuel injection assembly which eliminates the need for external high pressure lines or fittings that may rupture or leak.
A further object of the present invention is to provide a fuel injector assembly wherein the control of fuel pressure at the beginning of injection is not dependent upon engine speed and load.
Yet another object of the present invention is to provide a fuel injector assembly wherein the beginning of injection pressure may be controlled.
Another object of the present invention is to provide a fuel injector assembly wherein fuel pressure at the end of injection does not need to be reduced.
Yet a further object of the present invention is to provide a fuel injector assembly wherein the response during multiple injections during a single engine cycle is considerably faster than heretofore.
A further object of the present inventions is to provide a fuel injector assembly which eliminates cylinder-to-cylinder pressure variations.
Another object of the present invention is to provide a fuel injector assembly which increases fuel economy at high engine speeds and loads.
Still a further object of the present invention is to provide an internal combustion engine which includes a fuel injector assembly which achieves one or more of the foregoing objects.
This invention achieves these and other objects by providing a fuel injector assembly, comprising a pressurization control valve assembly, a timing control valve assembly and a pressure actuated needle valve. The pressure actuated needle valve provides a fuel outlet and a spring biased needle structured and arranged to be moved to an open position and a closed position relative to the fuel outlet and being positioned between the pressurization control valve assembly and the timing control valve assembly. Means are provided for selectively opening and closing the pressurization control valve assembly and the timing control valve assembly to control the pressure within the pressure actuated needle valve such that (a) when the pressurization control valve assembly is open and the timing control valve assembly is closed there will be pressure equilibrium within the pressure actuated needle valve and the spring will hold the needle in the closed position; (b) when the pressurization control valve assembly and timing control valve assembly are both closed, fuel in the pressure actuated needle valve will be pressurized, there will be pressure equilibrium within the pressure actuated needle valve, and the spring will continue to hold the needle in the closed position; (c) upon opening the timing control valve assembly, there will be a net force which will urge the needle in the open position; and (d) upon closing of the timing control valve assembly will there be a net force which will urge the needle in the closed postion.
This invention also achieves these and other objects by providing a fuel injector assembly which comprises a fuel injector housing comprising a plunger cavity and a first fuel chamber. A pressurization control valve assembly is provided which is structured and arranged for electrical connection to an electronic control module. The pressurization control valve assembly comprises a second fuel chamber, in fluidic communication with the first fuel chamber, and a first valve member and a second valve member. The first valve member is operable to open and close fuel flow between the first fuel chamber and the second fuel chamber in response to electronic control module signals. A control rod housing is provided which comprises a first pressure chamber, in fluidic communication with the plunger cavity, and a control rod cavity. A timing control valve assembly is provided which is structured and arranged for electrical connecion to an electronic control module and comprises a third valve member. A spill circuit conduit is provided which is in fluidic communication with the timing control valve assembly. A first fuel conduit extends between the first pressure chamber and the timing control valve assembly, the third valve member being operable to open and close fuel flow between the first fuel conduit and the spill circuit conduit in response to electronic control module signals. A needle assembly housing is provided which comprises a second pressure chamber, a needle cavity and a fuel outlet, the needle cavity comprising a first segment adjacent the control-rod cavity and a second segment in fluidic communication with the fuel outlet and the second pressure chamber. A second fuel conduit extends between the plunger cavity and the second pressure chamber. A plunger extends into the plunger cavity and is structured and arranged for reciprocating movement within the plunger cavity. An actuator is associated with the plunger and is structured and arranged for reciprocating the plunger in the plunger cavity. A control rod extends into the control rod cavity and includes a control rod segment, extending into the first segment of the needle cavity, and a control surface exposed to the first pressure chamber. The control rod is structured and arranged for reciprocating movement within the control rod cavity. A needle is provided having a first end extending into the first segment of the needle cavity, the first end including a first abutment surface engaging the control rod segment, and an opposite second end extending into the second segment of the needle cavity. The second end comprises a needle portion exposed to the second pressure chamber. The needle is structured and arranged for reciprocating movement within the needle cavity to open and close the fuel outlet. A third fuel conduit extends between the plunger cavity and the first fuel chamber, and a fourth fuel conduit extends between the second fuel chamber and a fuel supply conduit. A fifth fuel conduit extends between the first fuel chamber and the spill circuit conduit, the second valve member being operable to open and close fuel flow between the first fuel chamber and the spill circuit, when the first valve member is closed and opened, respectively.
An internal combustion engine which includes at least one piston which reciprocates within an engine cylinder and which includes a fuel injector assembly of the present invention is also provided.